Open AccessGenetic analysis of the β-lactamases of Mycobacterium tuberculosis and Mycobacterium smegmatis and susceptibility to β-lactam antibiotics
Author(s) -
Anthony R. Flores,
Linda M. Parsons,
Martin S. Pavelka
Publication year - 2005
Publication title -
microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.019
H-Index - 179
eISSN - 1465-2080
pISSN - 1350-0872
DOI - 10.1099/mic.0.27629-0
Subject(s) - mycobacterium smegmatis , microbiology and biotechnology , peptidoglycan , mycobacterium tuberculosis , antibiotics , mutant , biology , penicillin binding proteins , penicillin , cephalosporin , cefoxitin , bacteria , cell wall , biochemistry , tuberculosis , gene , genetics , medicine , staphylococcus aureus , pathology
Mycobacteria produce β -lactamases and are intrinsically resistant to β -lactam antibiotics. In addition to the β -lactamases, cell envelope permeability and variations in certain peptidoglycan biosynthetic enzymes are believed to contribute to β -lactam resistance in these organisms. To allow the study of these additional mechanisms, mutants of the major β -lactamases, BlaC and BlaS, were generated in the pathogenic Mycobacterium tuberculosis strain H37Rv and the model organism Mycobacterium smegmatis strain PM274. The mutants M. tuberculosis PM638 (Δ blaC1 ) and M. smegmatis PM759 (Δ blaS1 ) showed an increase in susceptibility to β -lactam antibiotics, as determined by disc diffusion and minimal inhibitory concentration (MIC) assays. The susceptibility of the mutants, as assayed by disc diffusion tests, to penicillin-type β -lactam antibiotics was affected most, compared to the cephalosporin-type β -lactam antibiotics. The M. tuberculosis mutant had no detectable β -lactamase activity, while the M. smegmatis mutant had a residual type 1 β -lactamase activity. We identified a gene, blaE , encoding a putative cephalosporinase in M. smegmatis . A double β -lactamase mutant of M. smegmatis , PM976 (Δ blaS1 Δ blaE : : res ), had no detectable β -lactamase activity, but its susceptibility to β -lactam antibiotics was not significantly different from that of the Δ blaS1 parental strain, PM759. The mutants generated in this study will help determine the contribution of other β -lactam resistance mechanisms in addition to serving as tools to study the biology of peptidoglycan biosynthesis in these organisms.